The invention relates to a display device, and more particularly to a switching device of a pixel electrode and methods for fabricating the same.
Bottom-gate type thin film transistors (TFTs) are widely used for thin film transistor liquid crystal displays (TFT-LCDs). FIG. 1 is a sectional view of a conventional bottom-gate type TFT structure 100. The TFT structure 100 typically comprises a glass substrate 110, a gate 120, a gate-insulating layer 130, a channel layer 140, an ohmic contact layer 150, a source 160 and a drain 170.
As the size of TFT-LCD panels increases, metals having low resistance are required. For example, gate lines employ low resistance metals such as Cu and Cu alloy in order to improve operation of the TFT-LCD. However, Cu has unstable properties such as poor adhesion with the glass substrate. The poor adhesion may cause peeling. Cu also has a tendency to diffuse into a gate-insulating film (such as silicon-oxide film), affecting the quality of the TFT device. Moreover, Cu is vulnerable to deformation. Specifically, in plasma (such as plasma enhanced chemical vapor deposition, PECVD) deposition, characteristic degradation such as roughness and resistance to Cu are increased due to Cu reacting with the gas used.
U.S. Pat. No. 6,562,668 to Jang et al., the entirety of which is hereby incorporated by reference, discloses a method of forming a TFT. The method uses an aluminum oxide or aluminum nitride layer as an adhesion layer between a Cu gate and a glass substrate and a cap layer covering the Cu gate.